Method for the terrestrially transmitting digital signals

ABSTRACT

A method is proposed that is used for terrestrial transmission of at least one digital signal, in particular a digital radio and/or TV broadcasting signal. In this method, the at least one digital signal, reduced in its data quantity by coding, is modulated, preferably by the OFDM method, and converted into the frequency position of at least one channel, adjacent to at least one occupied or unoccupied channel ( 30, 32 ) for transmitting an analog TV broadcasting signal, and is broadcast in this frequency position. The dynamic scope and the amplitude of the spectrum ( 41 ) of the at least one digital signal must undershoot a respectively predetermined value that is markedly less than the dynamic scope or amplitude of the video carrier of the spectrum ( 35, 36 ) of the analog TV broadcasting signal, so that there will be only slight intermodulation and cross modulation with other digital signals or with analog signals of other channels. The spectrum ( 41 ) of the at least one digital signal is transmitted, separated from at least one adjacent channel ( 30, 31 ) by a protective frequency margin ( 45 ). When a plurality of digital signals are transmitted in the at least one channel ( 31 ), the frequency ranges of at least two digital signals are transmitted, separated from one another by a protective frequency margin ( 50 ).

PRIOR ART

The invention is based on a method as generically defined by the mainclaim.

In terrestrial signal distribution of television signals, bothtopographic features and above all varying distances of the receiverfrom the various stations can create very great differences in fieldintensity at the reception site. The selectivity and linearity of thereceiver input stage are at best always limited, and as a result, whenall the theoretically possible TV channels and especially neighboring TVchannels are occupied with analog-modulated TV programs, problems canoccur because of excessive differences between the levels of the channelin use and the neighboring channel and because of cross modulation andintermodulation. The attempt is made to limit these problems by avoidingoccupation of neighboring channels. The neighboring channels that arethus not usable are also called forbidden channels. Because of the areacoverage and resultant overlaps among various stations for a certainregion, the result of this is that by far not all of the terrestriallypossible TV channels can be occupied. The resultant scarcity offrequencies is made even worse by the fact that for two stations thatare broadcasting the same program, different frequencies have to beprovided in the overlapping region, because otherwise common channelinterference such as ghost images as a rule occur, because ofdifferences in transit time and extinction zones from interference.

ADVANTAGES OF THE INVENTION

The method according to the invention having the characteristics of themain claim has the advantage over the prior art that the unusedforbidden channels can be occupied by digital signals, and in particulardigital radio and/or TV broadcasting signals, without causingsignificant intermodulation and cross modulation with other digitalsignals or with the analog signals of already-occupied channels. In thisway, markedly more channels can be used for terrestrial signaldistribution.

Advantageous further features of and improvements to the methoddisclosed in the main claim are possible by the provisions recited inthe dependent claims.

To reduce intermodulation and cross modulation, a modulation of thedigital signals by the OFDM method of claim 2 is advantageously used.

Claims 3 and 4 disclose the advantageous provision that at least onedigital signal be transmitted at relatively low levels. As a result, theanalog signals, which are more vulnerable to interference than digitalsignals, are not significantly impaired upon reception despite limitedselectivity on the part of the receiver input stage.

Reducing the quantity of data in accordance with claim 5 attains theadvantage that as many programs and/or data services as possible can beaccommodated in the forbidden channels.

The provision of a protective frequency margin between the frequencyrange of at least one digital signal and at least one neighboringchannel leads to an advantageous increase in protection frominterference, given the always-limited selectivity of receiver inputstages and decoding.

It is advantageous in accordance with claim 7 to use the same frequencyand the same channel for a program or data service in the broadcastingby various stations. In this way, the best possible increase in thenumber of programs for terrestrial signal distribution within aspecified frequency range is possible.

It is advantageous according to claim 8 to protect a plurality ofdigital data, radio and/or TV broadcasting signals against mutualinfluence on reception by using a protective frequency margin.

DRAWING

One exemplary embodiment of the invention is shown in the drawing anddescribed in further detail in the ensuing description.

FIG. 1 shows an apparatus for the terrestrial broadcasting of digitaldata, radio and/or TV broadcasting signals;

FIGS. 2 and 3 each show one example for occupying three adjacentchannels with analog and digital signal spectra;

FIG. 4 shows an apparatus for receiving the terrestrially transmitteddigital signals;

FIG. 5 shows a spectrum of a digital signal; and

FIG. 6 shows a channel occupation for the transmission of DVB signals.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

In FIG. 1, reference numeral 10 indicates a multiplexer, to which onedigital TV broadcasting signal each is supplied via a first, second andthird encoder 1, 2, and 3, and to which one digital radio signal each issupplied via a fourth through ninth encoder 4-9. The multiplexer 10 isconnected via modulator 15 and an amplifier 20 to a transmitting antennafor terrestrial broadcasting of the digital radio and TV broadcastingsignals.

The encoders 1-9 reduce the data quantity of the digital TV broadcastingsignals and digital radio signals, thus limiting the frequency spectraof the digital signals. For reducing the data quantity, data compressionalgorithms are suitable, such as MPEG 1, MPEG 2, or MPEG 4 (MPEG=motionpicture expert group). For audio data reduction, the ISO MPEG 11172standard, with its various layers, is suitable. The digital signalssupplied to the multiplexer 10 via the encoders 1-9 are combined in themultiplexer 10 by frequency multiplexing into a digital signal and thensubjected in the modulator 15 to a modulation process, such aspreferably th OFDM method (OFDM=orthogonal frequency divisionmultiplexing), and optionally also by a PSK method (PSK=phase shiftkeying) or a QAM method (QAM=quadrature amplitude modulation) withcarrier suppression. One goal of this provision is the realization of afrequency spectrum 41 of the digital signal in accordance with FIG. 5,with a dynamic scope 100 that undershoots a predetermined value in orderto reduce intermodulation and cross modulation with other digitalsignals or with analog signals. A further goal of this provision is tolimit the amplitude of the frequency spectrum 41 of the digital signalto a predetermined value, and to convert the digital signal to thefrequency position of a channel 31, which is adjoined in the directionof lower and higher frequencies by two channels 30 and 32 as shown inFIG. 2. The modulated digital signal is then adjusted in level, to avalue that as a rule can be markedly lower than the peak level of theanalog TV broadcasting signals, and broadcast from the transmittingantenna 25.

FIG. 2 shows an example of how the channel 31 for the digital signal,the channel 30 adjacent to it in the direction of lower frequencies foran analog TV broadcasting signal, and the channel 32 adjacent to it inthe direction of higher frequencies, also for an analog TV broadcastingsignal, are occupied. In the graph of FIG. 2, the amplitude A of thecorresponding frequency spectrum is plotted over the frequency f. In thedescription below, the adjacent analog channel 30 in the direction oflower frequencies will be called the first channel, the channel 31 forthe digital signal will be call the second channel, and the adjacentanalog channel 32 in the direction of higher frequencies will be calledthe third channel. The first channel 31 is limited by a lower limitfrequency f₁ and an upper limit frequency f₂ and includes the spectrum35 of a first analog TV broadcasting signal with a video carrier at thefrequency f_(T1). The third channel 32 is limited by a lower limitfrequency f₃ and an upper limit frequency f₄ and includes the spectrum36 of a second analog TV broadcasting signal with a video carrier at thefrequency f_(T2). The second channel 31 for the digital signal islimited by the upper limit frequency f₂ of the first channel 30 and thelower limit frequency f₃ of the third channel 32. The second channel 31,as a neighboring channel to two analog channels 30 and 32, is aso-called forbidden channel. The spectrum of the digital signal isdivided into four blocks, each separated from one another by aprotective frequency margin 50 having the frequency width f_(S2). Oneprotective frequency margin 45 each, whose frequency width is f_(S1), isprovided between the spectrum 41 of the digital signal and the upperlimit frequency f₂ of the first channel 30, and between that spectrumand the lower limit frequency f₃ of the third channel 32. At a frequencywidth of approximately 7 MHz for the second channel 31, this secondchannel 31 can be divided into four blocks, each of about 1.5 MHz, andthe remaining about 1 MHz can be used for the protective frequencymargins 50 between the individual blocks 40 and for the protectivefrequency margins 45 between the spectrum 41 of the digital signal andthe upper limit frequency f₂ of the first channel 30 and between thatspectrum and the lower limit frequency f₃ of the third channel 32.

At a frequency width of about 8 MHz for the second channel 31, thissecond channel 31 can again be divided into four blocks, each of about1.5 MHz, and the remaining about 2 MHz can be used for the protectivefrequency margins 50 between the individual blocks 40 and for theprotective frequency margins 45 between the spectrum 41 of the digitalsignal and the upper limit frequency f₂ of the first channel 30 andbetween that spectrum and the lower limit frequency f₃ of the thirdchannel 32. By means of the modulation in the modulator 15, the spectrum41 of the digital signal is limited to a predetermined value, which ismarkedly less than the amplitudes of the video carriers of the analog TVbroadcasting signals at the frequencies f_(T1) and f_(T2). Moreover, bythe modulation, the dynamic scope 100 and the amplitude of the spectrum41 of the digital signal are each limited to a predetermined value,which is markedly less than the dynamic scope and the amplitude of thevideo carrier of the spectra 35 and 35 of the analog signals of thefirst and third channels 30 and 32, respectively. In this way, there isonly slight intermodulation and cross modulation of the digital signalswith one another and with the analog signals of the first and thirdchannels 30 and 32. By the use of one of the above-named modulationmethods and by transmitting the digital signals at levels that aremarkedly lower than those of the analog signals, peak levels in thedigital signal are averted. This reduces interference in the analog TVbroadcasting signals in a receiver that has limited selectivity, andthis is also achieved through the protective frequency margins 45between the spectrum 41 of the digital signal and the upper limitfrequency f₂ of the first channel 30 and between that spectrum and thelower limit frequency f₃ of the third channel 32. The protectivefrequency margins 50 between the individual blocks of the spectrum 41 ofthe digital signal serve to protect the respective blocks, containingthe digital radio and/or TV broadcasting signals, from influencing oneanother. Influence on the digital signals in the receiver on the part ofthe analog TV broadcasting signals that occur and are received parallelto them has only a negligible effect, because of the greater securityagainst interference, given the selected digital signal transmission anddigital signal processing and given the use, which can be provided as anoption, of error-correction block methods, interleaving, and/or externalerror protection, such as of the Reed Solomon type. In each of the fourblocks 40 of FIG. 2, at least six audio/radio stereo programs can beaccommodated by data compression using ISO MPEG 11172 layer 2, or atleast one TV program can be transmitted by data compression using MPEG 1or 2. The ISO MPEG 11172 layer 3 standard allows the expansion, per1.5-MHz block 40, from six to up to twelve audio/radio programs at atransmission rate of 128 kB/s per audio/radio program, and the MPEG 4standard allows an expansion in the number of TV programs to at leasttwo per 1.5-MHz block. In the second channel 31 for the digital signal,other additional digital signals or other signal contents can also betransmitted individually or in blocks. These include, as examples, suchdata services as paging, message services, electronic newspapers,updates from data bases, traffic reports and visual traffic displays,stock-exchange data, transportation schedules, and so forth, as well asDVB signals (DVB=digital video broadcasting), which are currentlydefined for an 8-MHz raster, for occupying forbidden UHF channels. In adesign for a 7-MHz raster, it is also possible for the DVB signals tooccupy forbidden VHF channels. Then as shown in FIG. 6, oneself-contained coded frequency block 40 at a time is transmitted in thesecond channel 31, with protective frequency margins 45 from theadjacent channels 30 and 32.

The supplemental occupation of forbidden channels in regions that usethe PAL B/G standard can be quantified as follows:

Band I (VHF):

One additional 7-MHz channel, if only channel E2, which has a videocarrier frequency of 48.25 MHz, and channel E4, which has a videocarrier frequency of 62.25 MHz, are occupied with TV programs; and

two additional 7-MHz channels, if only channel E3, which has a videocarrier frequency of 55.25 MHz, is occupied.

Band IV (UHF):

Eight additional 8-MHz channels, or more, depending on the occupationwith analog modulated TV programs.

Band V (UHF):

Fourteen additional 8-MHz channels, or more, depending on the occupationwith analog modulated TV programs.

In a further exemplary embodiment according to FIG. 3, the occupation ofthe first channel 30 and the third channel 32 is achieved as in FIG. 2,each with the spectrum 35 and 36, respectively, of an analog TVbroadcasting signal. However, the spectrum 41 of the digital signal inthe second channel 31 is divided into three blocks, each separated fromone another by a respective protective frequency margin 50 with afrequency width f_(S2) and from the upper limit frequency f₂ of thefirst channel 30 and the lower limit frequency f₃ of the third channel,and by a protective frequency margin 45 with a frequency width f_(S1).This realization is appropriate, if a 6-MHz raster and a block width ofapproximately 1.5 MHz are used. The remaining approximately 1.5 MHz areused for the protective frequency margins 50 between the individualblocks 40 and for the protective frequency margins 45 between thespectrum 41 of the digital signal and the upper limit frequency f₂ ofthe first channel 30 and between that spectrum and the lower limitfrequency f₃ of the third channel 32.

The possibility also exists of selecting other block widths than 1.5MHZ, or even, as with DVB, of using the full second channel 31 in itsentirety from the outset.

When the OFDM modulation method is used, it becomes possible, bysimultaneous broadcasting, to use the same frequency in the same channelin the propagation region for the same program broadcast by differentstations.

In FIG. 4, reference numeral 55 indicates a receiver with a receivingantenna 60, which is connected to a demultiplexer 75 via a bandpassfilter 65 and a demodulator 70. The receiver 55 also includes a decoder80 for digital TV broadcasting signals and a decoder 81 for digitalradio signals. The decoder 80 for digital TV broadcasting signals issupplied with the digital TV broadcasting signals arriving from thedemultiplexer 75, and the decoder 81 for digital radio signals. Thedecoder 80 for digital radio signals is supplied with the digital radiosignals also arriving from the demultiplexer 75. The decoded digital TVbroadcasting signals are delivered to the digital input 86 of a TV set85, and the decoded digital radio signals are delivered to a speaker 95via an audio amplifier 90 to a speaker 95.

The signal received by the receiver 55 via the receiving antenna 60includes both the digital TV broadcasting signals and the digital radiosignals, which after being combined into a digital signal by the circuitof FIG. 1 have been broadcast terrestrially. In the bandpass filter 65,the second channel 31, in which this digital signal is transmitted, isselected. The selected digital signal is then delivered to thedemodulator 70, where it is demodulated. The demodulated digital signalis finally split in the demultiplexer 75 into two digital signals; theone digital signal contains the digital TV programs, and the otherdigital signal contains the digital audio/radio programs. In the decoder80 for digital TV programs and in the decoder 81 for digital audio/radioprograms, finally, the digital TV broadcasting signals and the digitalradio signals, respectively, are expanded. The expanded digital signalthat contains the digital TV broadcasting signals is then delivered tothe digital input 86 of the TB set 85, and there is split up into theindividual TV programs, subjected to a digital/analog conversion, andfinally reproduced in images and sound. The expanded digital signal thatthe digital radio signals contains is delivered to the audio amplifier90, split up there into the individual audio/radio programs, subjectedto a digital/analog conversion, amplified, and delivered to the speaker95 for audio reproduction.

In further embodiments of the method of the invention, only the dynamicscope 100 of the spectrum 41 of the digital signal is limited by themodulation to a predetermined value; in other embodiments, only alimitation of the amplitude of the digital spectrum 41 to apredetermined value takes place. In those cases, then as a rule agreater protective frequency margin 45 from the neighboring channels 30and 32 is present, or else receiver input stages with greaterselectivity are used.

What is claimed is:
 1. A method for terrestrial transmission of at leastone digital signal, in particular a digital radio and/or TV broadcastingsignal, comprising the steps of transmitting at least one digital signalover at least one channel which is adjacent to at least one occupied orunoccupied channel for transmitting an analog TV broadcasting signal;undershooting by the dynamic compass of the spectrum of the at least onedigital signal a predetermined value, which is markedly less than thedynamic compass of the spectrum of the analog TV broadcasting signal;and/or undershooting by the amplitude of the spectrum of the at leastone digital signal a predetermined value which is markedly less than theamplitude of the video carrier of the analog TV broadcasting signal. 2.A method as defined in claim 1, and further comprising transmitting theat least one digital signal modulated by the coded orthogonal frequencydivision multiplexing.
 3. A method as defined in claim 1, and furthercomprising transmitting the at least one digital signal at levels thatdo not exceed a predetermined value that is markedly lower than a peaklevel of the analog TV broadcasting signal.
 4. A method as defined inclaim 1, and further comprising reducing a data quantity of the at leastone digital signal by coding.
 5. A method as defined in claim 1, andfurther comprising transmitting a frequency range of the at least onedigital signal in the at least one channel separately from at least oneadjacent occupied or unoccupied channel by a protective frequencymargin.
 6. A method as defined in claim 1, and further comprisingbroadcasting a propagation region digital signals of identical content,modulated by coded orthogonal frequency division multiplexing, at a samefrequency and in a frequency range of the at least one channel.
 7. Amethod as defined in claim 1, and further comprising, upon transmissionof a plurality of individual digital signals or digital signals combinedinto blocks in the at least one channel, transmitting frequency rangesof at least two digital signals separated from one another by aprotective frequency margin.
 8. The method of claim 1, characterized inthat in the at least one channel (31), a self-contained coded frequencyblock (40), in particular containing DVB signals, is transmitted withprotective frequency margins (45) from the adjacent channels (30) and(32).
 9. A method for terrestrial transmission of at least one digitalsignal, in particular a digital radio and/or TV broadcasting signal,comprising the steps of transmitting at least one digital signal over atleast one channel (31), which is adjacent to at least one occupied orunoccupied channel (30, 32) for transmitting an analog TV broadcastingsignal; undershooting by the dynamic compass (100) of the spectrum (41)of the at least one digital signal a predetermined value, which ismarkedly less than the dynamic compass of the spectrum (35, 36) of theanalog TV broadcasting signal; undershooting by the amplitude of thespectrum (41) of the at least one digital signal a predetermined valuewhich is markedly less than the amplitude of the video carrier of theanalog TV broadcasting signal; and receiving the at least one digitalsignal at a level that is lower by up to approximately 20 db than thepeak level of the analog TV broadcasting signal.
 10. A method forterrestrial transmission of at least one digital signal, in particular adigital radio and/or TV broadcasting signal, comprising the steps oftransmitting at least one digital signal over at least one channel (31),which is adjacent to at least one occupied or unoccupied channel (30,32) for transmitting an analog TV broadcasting signal; undershooting bythe dynamic compass (100) of the spectrum (41) of the at least onedigital signal a predetermined value, which is markedly less than thedynamic compass of the spectrum (35, 36) of the analog TV broadcastingsignal; undershooting by the amplitude of the spectrum (41) of the atleast one digital signal a predetermined value which is markedly lessthan the amplitude of the video carrier of the analog TV broadcastingsignal,; dividing the at least one channel (31), for a channel width ofapproximately 6 MHz, into three blocks (40) approximately 1.5 MHz each,and utilizing the remaining approximately 1.5 MHz as protectivefrequency margins (50) between the individual blocks (40) and asprotective frequency margins (45) between the frequency range of thedigital spectrum (41) and one upper and one lower neighboring channel(32) and (30).
 11. A method for terrestrial transmission of at least onedigital signal, in particular a digital radio and/or TV broadcastingsignal, comprising the steps of transmitting at least one digital signalover at least one channel (31), which is adjacent to at least oneoccupied or unoccupied channel (30, 32) for transmitting an analog TVbroadcasting signal; that the dynamic compass (100) of the spectrum (41)of the at least one digital signal undershoots a predetermined value,which is markedly less than the dynamic compass of the spectrum (35, 36)of the analog TV broadcasting signal; undershooting by the amplitude ofthe spectrum (41) of the at least one digital signal a predeterminedvalue which is markedly less than the amplitude of the video carrier ofthe analog TV broadcasting signal, dividing the at least one channel(31), for a channel width of approximately 7 MHz, into four blocks (40)of approximately 1.5 MHz each, and utilizing the remaining 1 MHz asprotective frequency margins (50) between the individual blocks (40) andas a protective frequency margins (45) between the frequency range ofthe digital spectrum (41) and the upper and lower neighboring channels(32) and (30).
 12. A method for terrestrial transmission of at least onedigital signal, in particular a digital radio and/or TV broadcasting,comprising the steps of transmitting the at least one digital signalover at least one channel (31), which is adjacent to at least oneoccupied or unoccupied channel (30, 32) for transmitting an analog TVbroadcasting signal; undershooting by the dynamic compass (100) of thespectrum (41) of the at least one digital signal a predetermined value,which is markedly less than the dynamic compass of the spectrum (35, 36)of the analog TV broadcasting signal; and/or undershooting by theamplitude of the spectrum (41) of the at least one digital signal apredetermined value which is markedly less than the amplitude of thevideo carrier of the analog TV broadcasting signal, dividing the atleast one channel (31), for a channel width of approximately 8 MHz, intofour blocks (40) of approximately 1.5 MHz each, and the remainingapproximately 2 MHz as protective frequency margins (50) between theindividual blocks (40) and as protective frequency margins (45) betweenthe frequency range of the digital spectrum (41) and the upper and lowerneighboring channels (32) and (30).